Recording surface relief microstructure

Abstract

A method of recording a surface relief microstructure in a record medium includes: i) causing a coherent reconstruction or replay beam to impinge on a holographic optical element assembly, the holographic optical element assembly including a holographic optical element (HOE), the assembly causing selected portions of the beam to interfere at a focal region after diffraction by the holographic optical element so as to reconstruct a real image of an aperture previously used to construct the HOE; ii) locating a record medium at the focal region so that the real image is recorded; and, iii) causing relative movement between the record medium and the interfering beam portions and repeating steps i) and ii) so that the real image is recorded at a plurality of locations or pixels on the record medium.

We claim:  
     
       1. A method of recording a surface relief microstructure in a record medium, the method comprising: 
       i) causing a coherent reconstruction or replay beam to impinge on a holographic optical element assembly, the holographic optical element assembly including a holographic optical element (HOE), the assembly causing selected portions of the beam to interfere at a focal region after diffraction by the holographic optical element so as to reconstruct a real image of an aperture previously used to construct the HOE;  
       ii) locating a record medium at the focal region so that the real image is recorded; and,  
       iii) causing relative movement between the record medium and the interfering beam portions and repeating steps i) and ii) so that the real image is recorded at a plurality of locations or pixels on the record medium; wherein the holographic optical element assembly further includes an aperture mask for selecting the beam portions by defining suitable selecting apertures.  
     
     
       2. A method according to  claim 1 , wherein the holographic optical element is constructed so as to generate a real image of an aperture having a non-circular shape. 
     
     
       3. A method according to  claim 2 , wherein the aperture is in the shape of a polygon or an indicium. 
     
     
       4. A method according to  claim 1 , wherein the aperture is a pinhole. 
     
     
       5. A method according to  claim 1 , wherein the holographic optical element is constructed and illuminated such that the beam portions impinge on the record medium at angles on the same side of a normal to the record medium. 
     
     
       6. A method according to  claim 1 , wherein the aperture mask is a spatial light modulator such as a liquid crystal display. 
     
     
       7. A method according to  claim 1 , wherein the holographic optical element assembly further includes a diffraction grating and a screen arranged so that only first order diffracted beams from the diffraction grating pass through the HOE. 
     
     
       8. A method according to  claim 1 , wherein only two portions of the beam impinge on the record medium, the portions lying in a plane substantially orthogonal to the plane of the record medium. 
     
     
       9. A method according to  claim 1 , wherein only two portions of the beam impinge on the record medium, the portions lying in a plane which is rotated relative to the record medium for different locations such that resulting interference fringes are recorded in a range of directions of rotation relative to the record medium. 
     
     
       10. A method according to  claim 1 , wherein more than two portions of the beam impinge on the record medium. 
     
     
       11. A method according to  claim 10 , wherein, for a set of locations, a common reference beam portion is caused to interfere with respective different “object” beam portions. 
     
     
       12. A method according to  claim 9 , wherein only two portions of the beam impinge on the record medium, the portions lying in a plane which is rotated relative to the record medium for different locations such that resulting interference fringes are recorded in a range of directions of rotation relative to the record medium, wherein the “object” beam portions originate from positions on the HOE around a reference beam position. 
     
     
       13. A method according to  claim 1 , wherein the beam portions have different intensities. 
     
     
       14. A method according to  claim 1 , further comprising recording a 3D holographic image into the record medium in register with the real image pixels.